Comment on wat

• wonderingwanderer@sopuli.xyz ⁨2⁩ ⁨days⁩ ago

  I’m thankful we still live in a time when we can see the rest of the universe.

  Do we though? How do you know our entire known universe isn’t just a local cluster?

  If we could see the entire universe, then somewhere in the center we’d be able to point to the origin of the Big Bang. Since we can’t, that implies we’re only looking at a section of the universe analogous to a portion of the surface of a globe.

  source

  • SpacetimeMachine@lemmy.world ⁨2⁩ ⁨days⁩ ago

    Someone else already replied probably better than I can, but this is one of my favorite subjects to study.

    The big bang didn’t really start in a place, it happened at a point in time. As we look at all of the galaxies around us (minus the close ones we are gravitationally interacting with) they are all moving away from us, so either 1) we are exactly where the big bang took place (vanishingly unlikely) or 2) the big bang happened everywhere and all of space is expanding from that event.

    We can actually see the first light ever released in the universe (not from the big bang, as the universe was a dense plasma for the first ~400,000 years until the recombination era) as the cosmic microwave background radiation. And it is (relatively) even in all directions, minus some minor temperature variations.

    I highly suggest looking at a channel on YouTube called PBS Spacetime. They have videos going back years and years that dive into great depth on all of these topics!

    source

    • wonderingwanderer@sopuli.xyz ⁨1⁩ ⁨day⁩ ago

      Yes, I already responded to the other comment. Summarily, I don’t find their argument convincing.

      To add, it’s not surprising that everything is moving away from us. To use the other commenter’s balloon analogy, as the balloon expands, so do the circumference and surface area. So any two points on that surface will be moving away from each other as it does so.

      It’s also not surprising that the cosmic microwave background radiation appears relatively uniform. 14 billion years of expansion, and we can only observe or “neighborhood” of the universe, mind-bogglingly large as even that is. 14 billion years of moving on a more or less stable trajectory. We can’t see far enough backwards to view the origin point.

      Also, if the background radiation came from the big bang, then it would have outpaced us as our galaxy slowed down and the radiation continued moving at the speed of light. This suggests that the background radiation we witness was emitted after the energy that coalesced into our galaxy, and is just now catching up/surpassing us. Unless it’s reflecting off of something further outward, and on it’s way back.

      Is there any known pattern to the actual direction of cosmic background radiation? Is it aligned in any way or more or less random?

      source

      • SpacetimeMachine@lemmy.world ⁨1⁩ ⁨day⁩ ago

        The CMBR was the first light that could ever actually go a long distance in the universe, as before that the universe was opaque plasma. When the universe cooled to a threshold it the. Became transparent to light. This light was released in all directions at all points, which is why we still see it today. It will be detectable until the universe’s expansion speeds up to a point where it outpaces the speed of light.

        There are some patterns in the CMBR but only due to density fluctuations. A fascinating topic to look into is the Baryon Acoustic Oscillations. Small quantum density variations that were expanded rapidly as the big bang started going into overdrive that have shaped the universe on an immense scale.

        I don’t have time to answer every question you have sadly, and I’m just someone who really enjoys learning about this stuff in their free time. The channel I mentioned has videos on all of this. I highly suggest you start watching those if you actually want an in depth understanding of this.

        source
      • derek@infosec.pub ⁨1⁩ ⁨day⁩ ago

        The way you’re talking about the CMB and the questions you’re asking about it suggest that you’re unfamiliar with the topic’s particulars. I’d start here: en.wikipedia.org/…/Cosmic_microwave_background

        You’re making intuitive assumptions based in what you currently believe you know. Some of the concepts you’re using to framework your thinking simply don’t apply.

        source

        • -> View More Comments
  • thebestaquaman@lemmy.world ⁨2⁩ ⁨days⁩ ago

    By the nature of the Big Bang and the expansion of the universe, everywhere is at the origin. That is, if we believe that the universe started out as a singularity, and that the expansion of space itself is what causes that singularity to grow, then every point in the universe originated from the exact same point, and that nothing has “moved”, in the sense that the point itself is expanding. Thus, every place is at the “origin”.

    To use the balloon analogy: Draw a small dot on the balloon, that dot is the entire universe as a singularity. Now, inflate the balloon so the dot grows, and try to determine the “origin” of the dot. Of course, you could point to the centre of the dot, but I would argue that if the initial dot is infinitely small (a singularity) then every point on the expanded dot in fact originates from the exact same point.

    This does cause a bit of a headache because we’re arguing that a zero-dimensional thing suddenly became 3-dimensional. I’m honestly not sure how astrophysicists reconcile that, but I seem to remember reading that they boil down to saying “we know what happened <some extremely short time> after the Big Bang, but we don’t really know anything about what happened at t=0” per my understanding, even the concept of time breaks down when you go to t=0, so it becomes impossible to get to t = 0 + h.

    source

    • wonderingwanderer@sopuli.xyz ⁨1⁩ ⁨day⁩ ago

      That doesn’t make any sense, down to the geometric level.

      By the nature of expansion itself, there is an origin point somewhere in the center. That holds especially true in the case of uniform expansion.

      If “every point in the universe originated from the exact same point” then that origin point is somewhere in the center of the universe, and tracing the trajectories of every point backwards should intersect somewhere very close to that point.

      Your balloon analogy supports this thesis. No matter how much the dot expands, the center of the dot is where it originated. Yes, every point on the expanded dot originates from the same point. That point is in the center.

      Saying “sometimes physics is mindboggling” in order to rationalize invalid leaps is not a strong argument. Yes, sometimes physics is mindboggling. But that’s no reason to handwave away inconvenient facts whenever we’re trying to argue for something illogical. You need rigorous evidential support to justify a mindboggling conclusion, as is the case with quantum mechanics. Speculative or theoretical physics however cannot simply fill in the gaps with this sort of handwaving.

      Honestly, if the concept of time breaks down when you look at t=0, then that only tells me that the idea of t=0 itself is invalid and needs to be abandoned. Especially since there’s no evidential support for that theory, it’s entirely speculative, and has only been justified with the explanation that “We don’t have any better ideas.”

      Time didn’t just magically start at some random point before which time didn’t exist. And space didn’t just magically expand into 3 dimensions before which there was only 0. Energy and matter didn’t just suddenly appear without any prior cause initiating some action. All of those things would require violations of the laws of thermodynamics. And in the absence of far more evidence than ever has or even can be found, this “best guess” is full of more holes than many people seem ready to admit…

      source

      • thebestaquaman@lemmy.world ⁨1⁩ ⁨day⁩ ago

        If “every point in the universe originated from the exact same point” then that origin point is somewhere in the center of the universe

        This is where I’m disagreeing. Since space itself is expanding, every point “originated” where it currently sits, and has “expanded in place” so to speak. You can’t really imagine this as an expanding bubble (the balloon analogy was bad here), since a bubble necessarily expands into existing space. In our case, the bubble itself is the space.

        tracing the trajectories of every point backwards should intersect somewhere very close to that point.

        That’s where you get a problem. Space is expanding, so if you pick an arbitrary point in space, you’ll observe that the universe appears to be expanding out from that point. No matter where you are, and what direction you look, you will see that everything is moving away from you. Thus, if you reverse that process to “trace it backwards”, then no matter where you stand, you’ll see everything contracting towards you, and conclude that you are at the centre. For reference, Hubble agrees with this interpretation.

        Saying “sometimes physics is mindboggling” in order to rationalize invalid leaps is not a strong argument.

        I’m not trying to make any bombastic claims and hand-wave them away with “physics is hard”. I’m trying to give an accurate recollection of the current consensus based on my own understanding of it (which is rudimentary at best).

        Honestly, if the concept of time breaks down when you look at t=0, then that only tells me that the idea of t=0 itself is invalid and needs to be abandoned.

        It breaks down within our current models. You can of course always ask the question of “what happened before X”, and the answer today is that our current models can take us more or less arbitrarily close to a singularity (t=0), but not all the way there. There are several theories out there regarding what the “initial state” was.

        Time didn’t just magically start at some random point before which time didn’t exist. And space didn’t just magically expand into 3 dimensions before which there was only 0. (…)

        I’m not really saying it did. I’m saying that, as far as I know, we have no better model or understanding than that if we extrapolate to t=0, we get a singularity (0 D), that for some unknown reason “magically” started expanding into the 4 D space-time we inhabit today. The fact that this process violates pretty much every known law of nature really just means there’s something here we don’t understand yet. I believe it’s pretty well established that our current models more or less completely break down at around the Planck time (see the “in cosmology” section).

        source

        • -> View More Comments
      • SpacetimeMachine@lemmy.world ⁨1⁩ ⁨day⁩ ago

        I think the balloon analogy does not work well here. As far as we know the big bang was the start of our universes spacetime. There are plenty of theories on what might have happened “before.”.

        Here is a good playlist to get you started on learning some more info.

        youtube.com/playlist?list=PLsPUh22kYmNAV2T4af0Di7…

        And this video from that playlist is directly related to this discussion.

        youtu.be/K8gV05nS7mc

        source